Optical pickup

ABSTRACT

An object of the invention is to provide an optical pick-up device for recording and reproducing information through the use of holography, which can prevent deterioration of recording and reproduction accuracy due to vibrations from exterior or fluctuations in the relative positional relationship with a recording medium.  
     The optical pick-up device ( 11 ) comprises: a pick-up body ( 12 ) for recording information on an optical information recording medium ( 1 ) and reproducing information from the optical information recording medium ( 1 ) through the use of holography; and a position adjusting device for adjusting the position of the pick-up body ( 12 ) in order to correct a shift in the relative positional relationship between the pick-up body ( 12 ) and the optical information recording medium ( 1 ). The position adjusting device changes the position of the pick-up body ( 12 ) in a direction perpendicular to a surface of the optical information recording medium ( 1 ), in a direction parallel to the surface of the optical information recording medium ( 1 ), and in such a direction as to change the inclination of the pick-up body ( 12 ) with respect to the surface of the optical information recording medium ( 1 ).

TECHNICAL FIELD

[0001] The present invention relates to an optical pick-up device whichat least either records information on an optical information recordingmedium on which information is recorded through the use of holography,or reproduces information from the optical information recording medium.

BACKGROUND ART

[0002] Holographic recording for recording information on a recordingmedium through the use of holography is typically performed bysuperimposing light that carries image information on reference lightwithin the recording medium and by writing the resulting interferencepattern onto the recording medium. For reproducing the informationrecorded, the recording medium is irradiated with reference light sothat the image information is reproduced through diffraction derivedfrom the interference pattern.

[0003] Recently, volume holography, or digital volume holography inparticular, has been developed and is attracting attention in practicalfields for ultra-high density optical recording. Volume holography is amethod for writing a three-dimensional interference pattern by makingpositive use of a recording medium in the direction of thickness aswell, and is characterized in that it is possible to enhance thediffraction efficiency by increasing the thickness and to achieve agreater recording capacity by employing multiplex recording. Digitalvolume holography is a computer-oriented holographic recording methodwhich uses the same recording medium and recording method as with thevolume holography, whereas the image information to be recorded islimited to binary digital patterns. In the digital volume holography,analog image information such as a picture is once digitized anddeveloped into two-dimensional digital pattern information, and then itis recorded as image information. For reproduction, this digital patterninformation is read and decoded to restore the original imageinformation for display. Consequently, even if the SN ratio(signal-to-noise ratio) in the reproduction is somewhat poor, it ispossible to reproduce the original information with extremely highfidelity by performing differential detection and/or error correction onencoded binary data.

[0004] In conventional holographic recording, a recording medium itselfcontains no information intended for positioning. Therefore, positioningof information light and reference light with respect to the recordingmedium is possible only mechanically, which makes a precise positioningdifficult. On that account, the conventional holographic recording hassuch disadvantages that random access to the recording medium isdifficult and high density recording is also difficult.

[0005] Under the circumstances, it is conceivable that the recordingmedium intended for holographic recording may be formed into aplate-like ordinary optical disks such as a CD (compact disk), and arecording/reproducing apparatus intended for holographic recording maybe configured so that an optical pick-up device including an opticalsystem for recording information on and reproducing information from therecording medium is rendered movable with respect to the recordingmedium.

[0006] In ordinary optical disk devices, focus servo and tracking servoare performed typically by driving an objective lens in the opticalpick-up device. Under such configuration, vibrations externally appliedto the optical pick-up device cause relative vibrations between theobjective lens and the other parts in the optical system. Thosevibrations, even if they are of a magnitude as low as to beinsignificant to ordinary optical disk devices, affect the recording andreproduction operations greatly in the case of holographic recording.More specifically, in the case of holographic recording, even theslightest vibrations of the optical system under recording can cause alarge change in the interference pattern to thereby preclude accuraterecording of information. Under reproduction, a shift in positionalrelationship between the reference light for reproduction and theinterference pattern may hamper accurate reproduction of information.

[0007] Similarly, in holographic recording, a relative inclinationbetween the recording medium and the optical pick-up device has agreater impact than in ordinary optical disk devices.

[0008] Thus, in holographic recording, the use of an optical pick-updevice having the same structure as that of an ordinary optical diskdevice results in the problem that vibrations externally applied to theoptical pick-up device and fluctuations in the relative positionalrelationship between the optical pick-up device and the recording mediumdeteriorate recording and reproduction accuracies to a greater extentthan in the case of ordinary optical disk devices.

DISCLOSURE OF THE INVENTION

[0009] An object of the invention is to provide an optical pick-updevice for at least either recording information on an opticalinformation recording medium on which information is recorded throughthe use of holography, or reproducing information from the opticalinformation recording medium, which make it possible to preventdeterioration of recording and reproduction accuracy resulting fromexternal vibrations or fluctuations in the relative positionalrelationship with the recording medium.

[0010] An optical pick-up device of the invention comprises:

[0011] a pick-up body for at least either recording information on anoptical information recording medium on which information is recordedthrough the use of holography, or reproducing information from theoptical information recording medium; and

[0012] position adjusting means for adjusting a position of the pick-upbody in order to correct a shift in a relative positional relationshipbetween the pick-up body and the optical information recording medium.

[0013] In the optical pick-up device of the invention, the positionadjusting means adjusts the position of the pick-up body, whereby ashift in the relative positional relationship between the pick-up bodyand the optical information recording medium is corrected.

[0014] In the optical pick-up device of the invention, the positionadjusting means may change the position of the pick-up body in adirection perpendicular to a surface of the optical informationrecording medium, in a direction parallel to the surface of the opticalinformation recording medium, and in such a direction as to change aninclination of the pick-up body with respect to the surface of theoptical information recording medium.

[0015] In the optical pick-up device of the invention, the pick-up bodymay comprise: information light generation means for generatinginformation light carrying information; recording-specific referencelight generation means for generating recording-specific referencelight; and a recording optical system for irradiating the opticalinformation recording medium with the information light and therecording-specific reference light from the same side so thatinformation is recorded on the optical information recording medium inthe form of an interference pattern resulting from interference betweenthe information light and the recording-specific reference light. Inthis case, the recording optical system may perform the irradiation withthe information light and the recording-specific reference light so thatan optical axis of the information light and an optical axis of therecording-specific reference light are located on the same line.

[0016] In the optical pick-up device of the invention, the pick-up bodymay comprise: reproduction-specific reference light generation means forgenerating reproduction-specific reference light; a reproducing opticalsystem for irradiating the optical information recording medium with thereproduction-specific reference light and collecting reproduction lightgenerated from the optical information recording medium on the same sideas that from which the optical information recording medium isirradiated with the reproduction-specific reference light; and detectionmeans for detecting the reproduction light collected by the reproducingoptical system. In this case, the reproducing optical system may performthe irradiation with the reproduction-specific reference light and thecollection of the reproduction light so that an optical axis of thereproduction-specific reference light and an optical axis of thereproduction light are located on the same line.

[0017] In the optical pick-up device of the invention, the pick-up bodymay comprise: information light generation means for generatinginformation light carrying information; recording-specific referencelight generation means for generating recording-specific referencelight; reproduction-specific reference light generation means forgenerating reproduction-specific reference light; arecording/reproducing optical system for irradiating the opticalinformation recording medium with the information light and therecording-specific reference light from the same side so thatinformation is recorded on the optical information recording medium inthe form of an interference pattern resulting from interference betweenthe information light and the recording-specific reference light, andfor irradiating the optical information recording medium with thereproduction-specific reference light and collecting reproduction lightgenerated from the optical information recording medium on the same sideas that from which the optical information recording medium isirradiated with the reproduction-specific reference light; and detectionmeans for detecting the reproduction light collected by therecording/reproducing optical system. In this case, therecording/reproducing optical system may perform the irradiation withthe information light, the recording-specific reference light and thereproduction-specific reference light and the collection of thereproduction light so that an optical axis of the information light, anoptical axis of the recording-specific reference light, an optical axisof the reproduction-specific reference light, and an optical axis of thereproduction light are located on the same line. In addition, theinformation light generation means may modulate light spatially, and thedetection means may detect a spatial modulation pattern of light.

[0018] The other objects, features, and advantages of the invention willbecome fully apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is an explanatory diagram showing a schematic configurationof an optical pick-up device according to an embodiment of theinvention.

[0020]FIG. 2 is a block diagram showing a general configuration of anoptical information recording/reproducing apparatus including theoptical pick-up device according to the embodiment of the invention.

[0021]FIG. 3 is a plan view of a position adjusting device of theembodiment of the invention.

[0022]FIG. 4 is a perspective view showing a configuration of a lasercoupler of the embodiment of the invention.

[0023]FIG. 5 is a side view of the laser coupler of the embodiment ofthe invention.

[0024]FIG. 6 is a block diagram showing a configuration of a detectioncircuit of the embodiment of the invention.

[0025]FIGS. 7A through 7C are explanatory diagrams illustrating theprinciple of magneto-optic recording to be used in magnetic holography.

[0026]FIG. 8 is an explanatory diagram illustrating the principle ofreproduction of information in magnetic holography.

[0027]FIGS. 9A and 9B are explanatory diagrams showing how informationis expressed in the embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0028] Embodiments of the invention will now be described in detail withreference to the drawings.

[0029]FIG. 1 is an explanatory diagram showing a schematic configurationof an optical pick-up device according to an embodiment of theinvention. FIG. 2 is a block diagram showing a general configuration ofan optical information recording/reproducing apparatus including theoptical pick-up device according to the embodiment.

[0030] Reference is now made to FIG. 1 to describe a configuration of anoptical information recording medium in the present embodiment. Theoptical information recording medium 1 is made up of an informationrecording layer 3 on which information is recorded through the use ofvolume holography, a reflection film 5, and a protection layer 4 thatare stacked in this order on one surface of a disk-like transparentsubstrate 2 made of polycarbonate or the like. A plurality of addressservo areas 6 serving as positioning areas extending linearly in radialdirections are provided at predetermined angular intervals on theinterface between the information recording layer 3 and the protectionlayer 4. Sections in the form of sectors between adjacent ones of theaddress servo areas 6 are provided as data areas 7. On the address servoareas 6, information for performing focus servo and tracking servo undera sampled servo system and address information are recorded in advancein the form of emboss pits or the like. The focus servo can be performedby using a reflecting surface of the reflection film 5. For example,wobble pits may be used as the information for performing trackingservo. The transparent substrate 2 has an appropriate thickness of 0.6mm or less, for example. The information recording layer 3 has anappropriate thickness of 10 μm or more, for example. The informationrecording layer 3 is made of a magneto-optic recording material, onwhich information is recorded in the form of distribution patterns ofmagnetization through the use of holography. The information recordinglayer 3 may be made of a typical magneto-optic recording material suchas a TbFeCo-based amorphous film. Besides, a granular film, a magneticfilm having pinning sites, and magnetic photonic crystal may also beused. The reflection film 5 is made of aluminum, for example.

[0031] Reference is now made to FIG. 2 to describe the configuration ofthe optical information recording/reproducing apparatus. The opticalinformation recording/reproducing apparatus 10 comprises: a spindle 81on which the optical information recording medium 1 is mounted; aspindle motor 82 for rotating the spindle 81; and a spindle servocircuit 83 for controlling the spindle motor 82 so that the rotatingspeed of the optical information recording medium 1 is kept at apredetermined value. The optical information recording/reproducingapparatus 10 further comprises: an optical pick-up device 11 forirradiating the optical information recording medium 1 with informationlight and recording-specific reference light to record information, andirradiating the optical information recording medium 1 withreproduction-specific reference light and detecting reproduction lightto reproduce information recorded on the optical information recordingmedium 1; an electromagnetic coil 30 located to oppose to the opticalpick-up device 11 with the optical information recording medium 1 inbetween; and a driving device 84 for allowing the optical pick-up device11 and the electromagnetic coil 30 to be integrally movable in adirection of the radius of the optical information recording medium 1.

[0032] The optical information recording/reproducing apparatus 10further comprises: a detection circuit 85 for detecting a focus errorsignal FE, a tracking error signal TE, and a reproduction signal RF froman output signal of the optical pick-up device 11; a focus servo circuit86 for performing focus servo by moving a pick-up body to be describedlater in the optical pick-up device 11 in a direction of the thicknessof the optical information recording medium 1 based on the focus errorsignal FE detected by the detection circuit 85; a tracking servo circuit87 for performing tracking servo by moving the pick-up body in adirection of the radius of the optical information recording medium 1based on the tracking error signal TE detected by the detection circuit85; and a slide servo circuit 88 for performing slide servo bycontrolling the driving device 84 based on the tracking error signal TEand a command from a controller to be described later to move theoptical pick-up device 11 in a direction of the radius of the opticalinformation recording medium 1.

[0033] The optical information recording/reproducing apparatus 10further comprises: a signal processing circuit 89 for decoding theoutput data of a CCD array of the optical pick-up device 11 to bedescribed later to reproduce data recorded in the data areas 7 of theoptical information recording medium 1, and for reproducing a basicclock and determining addresses from the reproduction signal RF from thedetection circuit 85; a controller 90 for controlling the opticalinformation recording/reproducing apparatus 10 as a whole; and anoperating part 91 for giving various instructions to the controller 90.

[0034] The optical information recording/reproducing apparatus 10further comprises: an inclination detection circuit 92 for detecting arelative inclination between the optical information recording medium 1and the pick-up body; and an inclination correction circuit 93 forcorrecting the relative inclination between the optical informationrecording medium 1 and the pick-up body by changing the position of thepick-up body based on an output signal of the inclination detectioncircuit 92 in such a direction as to change the inclination of thepick-up body with respect to the surface of the optical informationrecording medium 1.

[0035] The controller 90 receives input of the basic clock and addressinformation outputted from the signal processing circuit 89, andcontrols the optical pick-up device 11, the spindle servo circuit 83,the slide servo circuit 88, and so on. The spindle servo circuit 83receives input of the basic clock outputted from the signal processingcircuit 89. The controller 90 has a CPU (Central Processing Unit), a ROM(Read Only Memory), and a RAM (Random Access Memory). Using the RAM as awork area, the CPU executes programs stored in the ROM to implement thefunctions of the controller 90.

[0036] Next, with reference to FIG. 1, description will be given of theconfiguration of the optical pick-up device 11 according to the presentembodiment. The optical pick-up device 11 has the pick-up body 12 forrecording information on the optical information recording medium 1 andreproducing information from the optical information recording medium 1.

[0037] The pick-up body 12 has a housing 13. A semiconductor substrate14 is fixed to the bottom inside the housing 13. A laser coupler 20, acollimator lens 15, and a prism block 16 are arranged in this order onthe semiconductor substrate 14. The laser coupler 20 and the prism block16 are directly fixed onto the semiconductor substrate 14. Thecollimator lens 15 is fixed to the semiconductor substrate 14 via a lensframe 15 a. The laser coupler 20 contains a semiconductor laser foremitting laser light, and an optical system and photodetectors fordetecting a focus error signal FE, a tracking error signal TE, and areproduction signal RF out of return light from the optical informationrecording medium 1. The configuration of the laser coupler 20 will bedetailed later.

[0038] The prism block 16 has a polarization beam splitter surface 16 aand a reflecting surface 16 b. Of the polarization beam splitter surface16 a and the reflecting surface 16 b, the polarization beam splittersurface 16 a is located closer to the collimator lens 15. Thepolarization beam splitter surface 16 a and the reflecting surface 16 bare arranged in parallel with each other, and the direction of thenormal of each of the surfaces 16 a and 16 b is inclined by 45° withrespect to the direction of the optical axis of the collimator lens 15.

[0039] In the semiconductor substrate 14, a spatial light modulator 18of reflective type is formed beneath the polarization beam splittersurface 16 a, and a CCD array 19 is formed beneath the reflectingsurface 16 b.

[0040] The spatial light modulator 18 has a number of pixels arranged ina matrix, and is capable of selecting whether or not to rotate thedirection of polarization of outgoing light by 90° with respect to thedirection of polarization of incident light pixel by pixel. For example,the spatial light modulator 18 may be a reflective liquid crystalelement which utilizes the optical rotary power of the liquid crystal,from which polarizing plates on both the incidence and outgoing sidesare removed. The spatial light modulator 18 constitutes the informationlight generation means, the recording-specific reference lightgeneration means, and the reproduction-specific reference lightgeneration means.

[0041] The CCD array 19 has a number of pixels arranged in a matrix. TheCCD array 19 corresponds to the detection means of the invention.

[0042] Moreover, an opening is formed in the top surface of the housing13 at a position opposite to the spatial light modulator 18 across thepolarization beam splitter surface 16 a. This opening is loaded with anobjective lens 17. The objective lens 17 is fixed to the housing 13 viaa lens frame 17 a.

[0043] Thus, the elements constituting the optical system of the opticalpick-up device 11 are all fixed to the housing 13 directly orindirectly.

[0044] Next, description will be given of the functions of the opticalsystem in the pick-up body 12. The laser coupler 20 emits coherentS-polarized light. Incidentally, S-polarization refers to linearpolarization the direction of which is perpendicular to the incidenceplane (plane of FIG. 1). P-polarization to be described later refers tolinear polarization the direction of which is parallel with theincidence plane.

[0045] The S-polarized laser light emitted from the laser coupler 20 iscollimated by the collimator lens 15, incident on the polarization beamsplitter surface 16 a of the prism block 16, reflected by thepolarization beam splitter surface 16 a and then incident on the spatiallight modulator 18. The emergent light from the spatial light modulator18 becomes P-polarized or S-polarized pixel by pixel. The emergent lightfrom the spatial light modulator 18 is incident on the polarization beamsplitter surface 16 a of the prism block 16 again. Of this light,S-polarized light is reflected by the polarization beam splitter surface16 a, and P-polarized light alone is transmitted through thepolarization beam splitter surface 16 a and incident on the objectivelens 17. The light incident on the objective lens 17 is condensed andprojected onto the optical information recording medium 1 so that itconverges on the interface between the information recording layer 3 andthe protection layer 4 of the optical information recording medium 1.This light is reflected by the reflection film 5 of the opticalinformation recording medium 1 and returns to the objective lens 17.

[0046] The return light from the optical information recording medium 1is collimated by the objective lens 17 and incident on the polarizationbeam splitter surface 16 a of the prism block 16. P-polarized componentsof this return light are transmitted through the polarization beamsplitter surface 16 a and incident on the spatial light modulator 18.The emergent light from the spatial light modulator 18 becomesP-polarized or S-polarized pixel by pixel. The emergent light from thespatial light modulator 18 is incident on the polarization beam splittersurface 16 a of the prism block 16 again. Of this light, S-polarizedlight is reflected by the polarization beam splitter surface 16 a andincident on the laser coupler 20. Meanwhile, S-polarized components ofthe return light from the optical information recording medium 1 arereflected by the polarization beam splitter surface 16 a, and arefurther reflected by the reflecting surface 16 b to be incident on theCCD array 19.

[0047] Reference is now made to FIG. 3 to describe a position adjustingdevice that adjusts the position of the pick-up body 12 in the opticalpick-up device 11 in order to correct a shift in the relative positionalrelationship between the pick-up body 12 and the optical informationrecording medium 1. FIG. 3 is a plan view of the position adjustingdevice.

[0048] In FIG. 3, the horizontal direction is the track direction. Theposition adjusting device has the following configuration. Elastic armfixing portions 140 a and 140 b are provided on both ends of the pick-upbody 12 in a direction orthogonal to the track direction. Elastic arms149 formed of an elastic member such as rubber, a plate spring, a coilspring and a wire are fixed to the elastic arm fixing portions 140 a and140 b at one of ends of each elastic arm 149. The other ends of theelastic arms 149 are fixed to a fixing wall 150 of the opticalinformation recording/reproducing apparatus.

[0049] Coils 151 and 152 for focus servo and inclination adjustment, andcoils 155 and 156 for tracking servo are attached to one end of thepick-up body 12 in the track direction. Similarly, coils 153 and 154 forfocus servo and inclination adjustment, and coils 157 and 158 fortracking servo are attached to the other end of the pick-up body 12 inthe track direction.

[0050] The position adjusting device has magnets 161, 162, 163, and 164arranged to penetrate through the coils 151, 152, 153, and 154,respectively, a magnet 165 located to face the coils 155 and 156, and amagnet 166 located to face the coils 157 and 158.

[0051] This position adjusting device is capable of changing theposition of the pick-up body 12 in a direction perpendicular to thesurface of the optical information recording medium 1 (directionperpendicular to the plane of FIG. 3), in a direction parallel to thesurface of the optical information recording medium 1 (verticaldirection in FIG. 3), and in such a direction as to change theinclination of the pick-up body 12 with respect to the surface of theoptical information recording medium 1.

[0052] The coils 151 to 154 of the position adjusting device are drivenby the focus servo circuit 86 and the inclination correction circuit 93shown in FIG. 2. On the other hand, the coils 155 to 158 are driven bythe tracking servo circuit 87 shown in FIG. 2.

[0053] Next, the laser coupler 20 will be described with reference toFIG. 4 through FIG. 6. FIG. 4 is a perspective view showing aconfiguration of the laser coupler 20. FIG. 5 is a side view of thelaser coupler 20. As shown in these diagrams, the laser coupler 20comprises: a semiconductor substrate 21 in which photodetectors 25 and26 are formed; a prism 22 located on this semiconductor substrate 21 soas to cover the photodetectors 25 and 26, being joined onto thesemiconductor substrate 21; a semiconductor device 23 located on thesemiconductor substrate 21 in a region other than a region where thephotodetectors 25 and 26 are formed, being joined onto the semiconductorsubstrate 21; and a semiconductor laser 24 joined onto the semiconductordevice 23. The semiconductor laser 24 horizontally emits forward laserlight toward the prism 22 and emits backward laser light in thedirection opposite to the forward laser light. The prism 22 has anoblique surface facing toward the semiconductor laser 24. This obliquesurface serves as a semi-reflecting surface 22 a that reflects part ofthe forward laser light from the semiconductor laser 24 to emit it inthe direction perpendicular to the semiconductor substrate 21, andtransmits part of the return light from the optical informationrecording medium 1. In addition, the top surface of the prism 22 servesas a total-reflecting surface 22 b that totally reflects the lightpassing through the prism 22 as shown in FIG. 5. The semiconductordevice 23 is provided with a photodetector 27 for receiving the backwardlaser light from the semiconductor laser 24. An output signal of thephotodetector 27 is used for automatic adjustment of the output of thesemiconductor laser 24. The semiconductor substrate 21 contains variousamplifiers and other electronic parts. The semiconductor device 23contains electronic parts such as an amplifier for driving thesemiconductor laser 24.

[0054] In the laser coupler 20 shown in FIGS. 4 and 5, part of theforward laser light from the semiconductor laser 24 is reflected by thesemi-reflecting surface 22 a of the prism 22 and incident on thecollimator lens 15 shown in FIG. 1. On the other hand, part of thereturn light from the optical information recording medium 1, condensedby the collimator lens 15, is transmitted through the semi-reflectingsurface 22 a of the prism 22 and introduced into the prism 22 toward thephotodetector 25. A semi-reflecting film is formed on the photodetector25. Part of the light introduced into the prism 22 is transmittedthrough the semi-reflecting film on the photodetector 25 and incident onthe photodetector 25. The rest of the light is reflected by thesemi-reflecting film on the photodetector 25, and is further reflectedby the total-reflecting surface 22 b of the prism 22 to be incident onthe photodetector 26.

[0055] Here, as shown in FIG. 5, the light introduced into the prism 22once converges halfway through the optical path between thephotodetectors 25 and 26. Then, the diameters of the incident light onthe photodetectors 25 and 26 coincide with each other when the lightfrom the laser coupler 20 converges on the interface between thehologram layer 3 and the protection layer 4 of the optical informationrecording medium 1, or in other words, when the light is in focus. Whenout of focus, the diameters of the incident light on the photodetectors25 and 26 differ from each other. Since the diameters of the incidentlight on the photodetectors 25 and 26 change in directions opposite toeach other, the focus error signal is obtainable by detecting signalscorresponding to the changes of the diameters of the incident light onthe photodetectors 25 and 26. As shown in FIG. 4, each of thephotodetectors 25 and 26 has three-way split light receiving portions.The light receiving portions of the photodetector 25 shall be A1, C1,and B1, and the light receiving portions of the photodetector 26 A2, C2,and B2. C1 and C2 are light receiving portions located at the centersbetween A1 and B1 and between A2 and B2, respectively. The split linesbetween the individual light receiving portions are arranged in parallelto the direction corresponding to the track direction of the opticalinformation recording medium 1. Consequently, from differences in outputbetween the light receiving portions A1 and B1 and between A2 and B2,the tracking error signal is obtainable by a push-pull method.

[0056]FIG. 6 is a block diagram showing a configuration of the detectioncircuit 85 for detecting the focus error signal, the tracking errorsignal, and the reproduction signal based on the outputs of thephotodetectors 25 and 26. The detection circuit 85 comprises: an adder31 for adding the outputs of the light receiving portions A1 and B1 ofthe photodetector 25; a gain adjusting amplifier 32 for adjusting thegain in the output of the adder 31; a gain adjusting amplifier 33 foradjusting the gain in the output of the light receiving portion C1 ofthe photodetector 25; a subtracter 34 for calculating a differencebetween the output of the gain adjusting amplifier 32 and the output ofthe gain adjusting amplifier 33; an adder 35 for adding the outputs ofthe light receiving portions A2 and B2 of the photodetector 26; a gainadjusting amplifier 36 for adjusting the gain in the output of the adder35; a gain adjusting amplifier 37 for adjusting the gain in the outputof the light receiving portion C2 of the photodetector 26; a subtracter38 for calculating a difference between the output of the gain adjustingamplifier 36 and the output of the gain adjusting amplifier 37; and asubtracter 39 for calculating a difference between the output of thesubtracter 34 and the output of the subtracter 38 to generate the focuserror signal FE.

[0057] The detection circuit 85 further comprises: a subtracter 40 forcalculating a difference between the output of the light receivingportion A1 and the output of the light receiving portion B1 of thephotodetector 25; a subtracter 41 for calculating a difference betweenthe output of the light receiving portion A2 and the output of the lightreceiving portion B2 of the photodetector 26; and a subtracter 42 forcalculating a difference between the output of the subtracter 40 and theoutput of the subtracter 41 to generate the tracking error signal TE.The detection circuit 85 further comprises: an adder 43 for adding theoutput of the adder 31 and the output of the light receiving portion C1;an adder 44 for adding the output of the adder 35 and the output of thelight receiving portion C2; and an adder 45 for adding the output of theadder 43 and the output of the adder 44 to generate the reproductionsignal RF. In the present embodiment, the reproduction signal RF is asignal which is the reproduction of the information recorded in theaddress servo areas 6 of the optical information recording medium 1.

[0058] Reference is now made to FIGS. 7A through 7C and FIG. 8 todescribe the principle of magnetic holography utilized in the presentembodiment. Magnetic holography is information recording technology thatcombines the characteristics of magneto-optic recording and holography.More specifically, in magnetic holography, information is recorded byforming distribution patterns of magnetization corresponding toholography-based interference patterns in an information recording layermade of a magneto-optic recording material.

[0059] First, the principle of magneto-optic recording used in magneticholography will be described with reference to FIGS. 7A through 7C. FIG.7A shows an information recording layer 51 made of a magneto-opticrecording material. The arrows in the information recording layer 51indicate directions of magnetization. In FIG. 7A, the directions ofmagnetization in the information recording layer 51 are all downward. Torecord information on the information recording layer 51, theinformation recording layer 51 is irradiated with laser light 52 at adesired portion as shown in FIG. 7B, and an external magnetic field inthe direction opposite to the directions of magnetization shown in FIG.7A is applied by an electromagnetic coil 53. In the informationrecording layer 51, the portion irradiated with the laser light 52reaches or exceeds Curie point in temperature, and the magnetizationdisappears. As shown in FIG. 7C, when the irradiation with the laserlight 52 is ended, the temperature in the portion having been irradiatedwith the laser light 52 falls to or below Curie point, and magnetizationis fixed in the same direction as that of the external magnetic field.In this way, in magneto-optic recording, the information recording layer51 is selectively irradiated with light to form a distribution patternof magnetization to thereby record information. The information recordedon the information recording layer 51 is reproduced through the use of amagneto-optic effect, i.e., Kerr effect or Faraday effect.

[0060] In magnetic holography, instead of selectively irradiating theinformation recording layer 51 with the laser light 52, aholography-based interference pattern is formed in the informationrecording layer 51. In this case, the information recording layer 51rises in temperature at portions of the interference pattern where thelight intensity is higher. Consequently, a distribution pattern ofmagnetization corresponding to the interference pattern is formed in theinformation recording layer 51.

[0061] Next, the principle of reproduction of information in magneticholography will be described with reference to FIG. 8. In FIG. 8, theinformation recording layer 51 has a distribution pattern ofmagnetization in which two types of band-shaped portions 51 a and 51 bthat are opposite in direction of magnetization are arrangedalternately. In FIG. 8, the direction in which the band-shaped portions51 a and 51 b are arranged is defined as X direction; the directionalong the lengths of the band-shaped portions 51 a and 51 b is definedas Y direction; and the direction orthogonal to the X and Y directionsis defined as Z direction.

[0062] It is here assumed that light linearly polarized in the Ydirection is incident on the information recording layer 51. In FIG. 8,the reference numerals 61A and 61B represent beams of the light incidenton the band-shaped portions 51 a and 51 b, respectively. The arrowsinside the ellipses drawn with alternate long and short dashed linesrepresent the directions of polarization. The directions of polarizationof the beams of light 62A and 62B having passed through the band-shapedportions 51 a and 51 b are rotated by a predetermined angle indirections opposite to each other due to Faraday effect. Consequently,the beams of light 62A and 62B bear Y-directional polarized componentsof the same magnitude and X-directional polarized components in oppositedirections. In FIG. 8, the reference numeral 64A indicates part of thebeams of light just having passed through the information recordinglayer 51, the part having a positive X-directional polarized component.The reference numeral 64B indicates another part of the beams of lightjust having passed through the information recording layer 51, the parthaving a negative X-directional polarized component.

[0063] Of the light having passed through the information recordinglayer 51, zeroth order diffracted light exhibits the Y-directionalpolarized component alone. On the other hand, first order diffractedlight of the light having passed through the information recording layer51 exhibits the X-directional polarized component alone. Therefore, ofthe light having passed through the information recording layer 51, thatconsisting of the X-directional polarized components is the lightdiffracted by the distribution pattern of magnetization, i.e.,holography-based interference pattern, of the information recordinglayer 51. This light serves as reproduction light that carries theinformation recorded on the information recording layer 51. Thus, in themagnetic holography, information can be reproduced by detecting lighthaving polarized components in the direction orthogonal to the directionof polarization of the light incident on the information recording layer51.

[0064] In FIG. 8, the distribution pattern of magnetization of theinformation recording layer 51 is a two-dimensional one. In the presentembodiment, however, three-dimensional distribution patterns ofmagnetization are formed in the information recording layer 3 of theoptical information recording medium 1 shown in FIG. 1. It is therebypossible to enhance the diffraction efficiency of the distributionpatterns of magnetization and to attain increased recording capacitythrough multiplex recording.

[0065] Reference is now made to FIGS. 9A and 9B to describe howinformation is expressed in the present embodiment. In the embodiment,intensity (amplitude) of light is spatially modulated to generateinformation light that carries information. In the embodiment, adjoiningtwo pixels express single-bit digital data of “1” or “0”. Morespecifically, as shown in FIG. 9A, one of the two pixels is darkened andthe other is brightened to express digital data “1”, and, as shown inFIG. 9B, the dark and bright are inverted to express digital data “0”.Two pixels both brightened or both darkened means error data.

[0066] Next, with reference to FIG. 1, description will be given of thefunctions of the optical information recording/reproducing apparatus 10according to the embodiment under servo, recording, and reproducingoperations, individually. Here, directions of magnetization in theinformation recording layer 3 of the optical information recordingmedium 1 shall be all identical initially.

[0067] First, the function under servo operation will be described.Under servo operation, the spatial light modulator 18 rotates, for everypixel, the direction of polarization of the emergent light by 90° withrespect to the direction of polarization of the incident light. Thepower of light emitted from the laser coupler 20 is set to a low levelfor reproduction. The controller 90 predicts the timing at which thelight that has exited from the objective lens 17 passes through theaddress servo areas 6 based on the basic clock reproduced from thereproduction signal RF, and maintains the foregoing setting while thelight from the objective lens 17 passes through the address servo areas6.

[0068] The S-polarized light emitted from the laser coupler 20 iscollimated by the collimator lens 15, incident on the polarization beamsplitter surface 16 a of the prism block 16, reflected by thepolarization beam splitter surface 16 a, and incident on the spatiallight modulator 18. The emergent light from the spatial light modulator18 is P-polarized for every pixel. The emergent light from the spatiallight modulator 18 is incident on the polarization beam splitter surface16 a of the prism block 16 again, transmitted through the same, andincident on the objective lens 17. The light incident on the objectivelens 17 is condensed and projected onto the optical informationrecording medium 1 so that it converges on the interface between theinformation recording layer 3 and the protection layer 4 of the opticalinformation recording medium 1. This light is reflected by thereflection film 5 of the optical information recording medium 1. At thistime, the light is modulated by the emboss pits in the address servoareas 6 and then returns to the objective lens 17.

[0069] The return light from the optical information recording medium 1is collimated by the objective lens 17 and incident on the polarizationbeam splitter surface 16 a of the prism block 16. P-polarized componentsof this return light are transmitted through the polarization beamsplitter surface 16 a, and then incident on the spatial light modulator18. The emergent light from the spatial light modulator 18 here isS-polarized light, which is reflected by the polarization beam splittersurface 16 a and incident on the laser coupler 20. The light incident onthe laser coupler 20 is detected by the photodetectors 25 and 26 in thelaser coupler 20. Then, based on the outputs of these photodetectors 25and 26, the focus error signal FE, the tracking error signal TE, and thereproduction signal RF are generated. Based on these signals, focusservo and tracking servo are performed, along with the generation of thebasic clock and the determination of addresses.

[0070] In the foregoing setting under the servo operation, theconfiguration of the optical pick-up device 11 is similar to that ofpick-ups intended for recording and reproduction with ordinary opticaldisks such as a CD (compact disk), a DVD (digital video disk or digitalversatile disk), and an HS (hyper storage disk). It is thereforepossible to configure the optical information recording/reproducingapparatus 10 of the present embodiment to have compatibility withordinary optical disk devices.

[0071] Next, description will be given of the function under recordingoperation. Under recording operation, the spatial light modulator 18selects, pixel by pixel, whether or not to rotate the direction ofpolarization of the emergent light by 90° with respect to the directionof polarization of the incident light. In addition, the electromagneticcoil 30 applies to the information recording layer 3 of the opticalinformation recording medium 1 an external magnetic field in thedirection opposite to the initial direction of magnetization of theinformation recording layer 3.

[0072] The power of light emitted from the laser coupler 20 is set toreach high levels on a pulse basis for recording. The controller 90predicts the timing at which the light that has exited from theobjective lens 17 passes through the data areas 7 based on the basicclock reproduced from the reproduction signal RF, and maintains theforegoing setting while the light from the objective lens 17 passesthrough the data areas 7. While the light from the objective lens 17passes through the data areas 7, neither focus servo nor tracking servois performed and the pick-up body 12 is fixed.

[0073] The S-polarized light emitted from the laser coupler 20 iscollimated by the collimator lens 15, incident on the polarization beamsplitter surface 16 a of the prism block 16, reflected by thepolarization beam splitter surface 16 a and incident on the spatiallight modulator 18. The emergent light from the spatial light modulator18 is P-polarized or S-polarized pixel by pixel. The emergent light fromthe spatial light modulator 18 is incident on the polarization beamsplitter surface 16 a of the prism block 16 again. Of this light,P-polarized light alone is transmitted through the polarization beamsplitter surface 16 a and incident on the objective lens 17. The lightincident on the objective lens 17 is condensed and projected onto theoptical information recording medium 1 so that it converges on theinterface between the information recording layer 3 and the protectionlayer 4 of the optical information recording medium 1. This light isreflected by the reflection film 5 of the optical information recordingmedium 1 and returns to the objective lens 17.

[0074] Under the recording operation, the light projected onto theinformation recording medium 1 is light which is spatially modulated inintensity. In the embodiment, this modulated light has functions of boththe information light and the recording-specific reference light. Thatis, when projected onto the information recording medium 1, thismodulated light passes through the information recording layer 3, isreflected by the reflection film 5, and then passes through theinformation recording layer 3 again. Here, the light that initiallypasses through the information recording layer 3 and the light thatpasses through the information recording layer 3 after being reflectedby the reflection film 5 interfere with each other to form athree-dimensional interference pattern. Consequently, one of these twokinds of light serves as the information light and the other as therecording-specific reference light.

[0075] In the information recording layer 3, the information light andthe recording-specific reference light interfere with each other to forma three-dimensional interference pattern. Then, when the power of thelight emitted from the laser coupler 20 reaches a high level, theinformation recording layer 3 rises in temperature at portions where thelight intensity is higher. Subsequent to that, when the temperature atthe portions drops following a shift of the irradiation target portion,the directions of magnetization are inverted. As a result, athree-dimensional distribution pattern of magnetization corresponding tothe interference pattern between the information light and therecording-specific reference light is formed in the informationrecording layer 3.

[0076] Next, description will be given of the function under reproducingoperation. Under reproducing operation, the spatial light modulator 18rotates, for every pixel, the direction of polarization of the emergentlight by 90° with respect to the direction of polarization of theincident light. Otherwise, in order to make the spatial frequency of thereproduction-specific reference light generally equal to the spatialfrequency of the recording-specific reference light, the direction ofpolarization of the emergent light may be switched alternately for eachpixel of the spatial light modulator light 18 to generatereproduction-specific reference light that is spatially modulated in acheckered pattern.

[0077] The power of the light emitted from the laser coupler 20 is setto a low level for reproduction. The controller 90 predicts the timingat which the light that has exited from the objective lens 17 passesthrough the data areas 7 based on the basic clock reproduced from thereproduction signal RF, and maintains the foregoing setting while thelight from the objective lens 17 passes through the data areas 7. Whilethe light from the objective lens 17 passes through the data areas 7,neither focus servo nor tracking servo is performed and the pick-up body12 is fixed.

[0078] The S-polarized light emitted from the laser coupler 20 iscollimated by the collimator lens 15, incident on the polarization beamsplitter surface 16 a of the prism block 16, reflected by thepolarization beam splitter surface 16 a, and incident on the spatiallight modulator 18. P-polarized light out of the emergent light from thespatial light modulator 18 is transmitted through the polarization beamsplitter surface 16 a of the prism block 16 to becomereproduction-specific reference light, which is incident on theobjective lens 17. This reproduction-specific reference light iscondensed and projected onto the optical information recording medium 1so that it converges on the interface between the information recordinglayer 3 and the protection layer 4 of the optical information recordingmedium 1. This light is reflected by the reflection film 5 of theoptical information recording medium 1 and passes through theinformation recording layer 3 again.

[0079] Here, the reproduction-specific reference light that first passesthrough the information recording layer 3 causes reproduction light thatproceeds toward the objective lens 17 from the information recordinglayer 3. On the other hand, the reproduction-specific reference lightthat passes through the information recording layer 3 after beingreflected by the reflection film 5 causes reproduction light thatproceeds toward the reflection film 5 from the information recordinglayer 3. This reproduction light is reflected by the reflection film 5and proceeds toward the objective lens 17.

[0080] The reproduction light is S-polarized. This reproduction light iscollimated by the objective lens 17, reflected by the polarization beamsplitter surface 16 a of the prism block 16, and is further reflected bythe reflecting surface 16 b to be incident on the CCD array 19. On theCCD array 19 is formed a spatial modulation pattern of the informationlight under the recording operation. This modulation pattern is detectedto reproduce the information.

[0081] As shown in FIG. 1, in the present embodiment, the irradiationwith the information light, the recording-specific reference light andthe reproduction-specific reference light, and the collection of thereproduction light are performed on the same side of the informationrecording layer 3 so that the optical axis of the information light, theoptical axis of the recording-specific reference light, the optical axisof the reproduction-specific reference light, and the optical axis ofthe reproduction light are located on the same line.

[0082] Next, with reference to FIG. 3, description will be given of thefunction of the position adjusting device in the optical pick-up device11 according to the present embodiment. The coils 151 to 154 of theposition adjusting device are driven by the focus servo circuit 86 andthe inclination correction circuit 93 shown in FIG. 2. On the otherhand, the coils 155 to 158 are driven by the tracking servo circuit 87shown in FIG. 2.

[0083] The focus servo circuit 86 drives the coils 151 to 154 based onthe focus error signal FE so that the positions of the coils 151 to 154change by the same amount in a direction perpendicular to the surface ofthe optical information recording medium 1 (direction perpendicular tothe plane of FIG. 3). The position of the pick-up body 12 is therebychanged in the direction perpendicular to the surface of the opticalinformation recording medium 1, and focus servo is performed.

[0084] The tracking servo circuit 87 drives the coils 155 to 158 basedon the tracking error signal TE so that the coils 155 to 158 aredisplaced in the same direction. The position of the pick-up body 12 isthereby changed in a direction orthogonal to the track of the opticalinformation recording medium 1, and tracking servo is performed.

[0085] The inclination correction circuit 93 drives the coils 151 to 154based on the results of detection of the inclination detection circuit92 so that at least one of the coils 151 to 154 differs from the rest ofthe coils in amount of displacement. The inclination of the pick-up body12 with respect to the surface of the optical information recordingmedium 1 is thereby changed to correct the relative inclination betweenthe optical information recording medium 1 and the pick-up body 12.

[0086] Relative inclinations between the optical information recordingmedium 1 and the pick-up body 12 include ones resulting from a tilt orcurve of the optical information recording medium 1 along the radialdirection (hereinafter referred to as radial tilt), and ones resultingfrom a tilt or curve of the optical information recording medium 1 alongthe circumferential direction (hereinafter referred to as tangentialtilt). Since the position adjusting device according to the presentembodiment is capable of inclining the pick-up body 12 in arbitrarydirections, it is possible to correct any relative inclination betweenthe optical information recording medium 1 and the pick-up body 12,including those resulting from the radial tilt and tangential tilt.

[0087] Here, description will be given of two examples of the method ofdetecting the relative inclination between the optical informationrecording medium 1 and the pick-up body 12 with the inclinationdetection circuit 92. In a first example, information for inclinationdetection is recorded on a plurality of predetermined locations in theoptical information recording medium 1 by using information lightmodulated in a checkered pattern and the recording-specific referencelight. Then, to detect inclination, the information for inclinationdetection is reproduced. When there is no relative inclination betweenthe optical information recording medium 1 and the pick-up body 12,differences in output between vertically- or horizontally-adjoining twopixels of the CCD array 19 become maximum. On the other hand, when arelative inclination occurs between the optical information recordingmedium 1 and the pick-up body 12, the differences in output betweenvertically- or horizontally-adjoining two pixels of the CCD array 19decrease. In the first example, the direction and magnitude of therelative inclination between the optical information recording medium 1and the pick-up body 12 are detected from a decrease in the differencein output between vertically-adjoining two pixels and a decrease in thedifference in output between horizontally-adjoining two pixels.

[0088] In a second example of the method for detecting an inclination, apredetermined pit pattern is formed on the optical information recordingmedium 1 in advance. This pattern is irradiated with light, and thediffracted light resulting from the pattern is received by aphotodetector having a plurality of split light receiving portions.Then, the direction of displacement and the amount of displacement ofthe diffracted light are detected from the outputs of this photodetectorwith reference to a state where there is no relative inclination betweenthe optical information recording medium 1 and the pick-up body 12. Thedirection and magnitude of the relative inclination between the opticalinformation recording medium 1 and the pick-up body 12 are therebydetected.

[0089] As has been described, the optical pick-up device 11 of thepresent embodiment comprises: the pick-up body 12 for at least eitherrecording information on the optical information recording medium 1 onwhich information is recorded through the use of holography, orreproducing information from the optical information recording medium 1;and the position adjusting device for adjusting the position of thepick-up body 12 in order to correct a shift in the relative positionalrelationship between the pick-up body 12 and the optical informationrecording medium 1. The elements constituting the optical system of theoptical pick-up device 11 are all fixed to the housing 13 directly orindirectly.

[0090] Consequently, according to the optical pick-up device 11 of theembodiment, vibrations externally applied to the optical pick-up device11 will not cause any of the elements constituting the optical system ofthe optical pick-up device 11 to vibrate relative to the rest. It istherefore possible to prevent recording and reproduction accuracy fromdeteriorating due to vibrations from exterior. Specifically, accordingto the embodiment, recording accuracy is improved because theinterference pattern formed in the information recording layer 3 of theoptical information recording medium 1 is stabilized under recordingoperation. Under reproducing operation, reproduction accuracy isimproved because changes in the positional relationship between thereproduction-specific reference light and the interference pattern aresuppressed.

[0091] Besides, according to the embodiment, a shift in the relativepositional relationship between the pick-up body 12 and the opticalinformation recording medium 1 is correctable with the positionadjusting device. It is therefore possible to prevent recording andreproduction accuracy from deteriorating due to fluctuations in therelative positional relationship between the pick-up body 12 and theoptical information recording medium 1.

[0092] In addition, according to the embodiment, even if the opticalinformation recording medium 1 expands/contracts to shrink or enlargethe modulation pattern of the reproduction light, it is possible tomaintain the modulation pattern of the reproduction light almostconstant in magnitude by adjusting the distance between the pick-up body12 and the optical information recording medium 1.

[0093] Moreover, according to the embodiment, the spatial lightmodulator 18 and the CCD array 19 are formed on the same semiconductorsubstrate 14. This makes it possible to ensure precise correspondencebetween the positions of the pixels of the spatial light modulator 18and the positions of the pixels of the CCD array 19, and to avoid achange in the correspondence.

[0094] Furthermore, according to the embodiment, the irradiation of theoptical information recording medium 1 with the recording-specificreference light and the information light for recording, and theirradiation of the optical information recording medium 1 with therecording-specific reference light and the collection of thereproduction light for reproduction are all performed from the same sideand on the same axis on the optical information recording medium 1. Thisallows a compact configuration of the optical system for recording andreproduction. In addition, according to the embodiment, it is possibleto configure the optical system for recording and reproduction in theform of the optical pick-up device 11 as with ordinary optical diskdevices. This facilitates random access to the optical informationrecording medium 1.

[0095] Additionally, according to the embodiment, information forperforming focus servo and tracking servo is recorded on the opticalinformation recording medium 1 so that this information can be used toperform focus servo and tracking servo. This allows a precisepositioning of the light for recording or reproduction, whichconsequently improves removability, facilitates random access, andincreases recording density, recording capacity and transfer rate.

[0096] Besides, according to the embodiment, information recorded in theform of emboss pits on a recording medium can be reproduced by bringingthe optical pick-up device 11 into a servo state. It is thereby possibleto attain compatibility with conventional optical disk devices.

[0097] Moreover, according to the optical informationrecording/reproducing apparatus 10 of the embodiment, athree-dimensional distribution pattern of magnetization corresponding toa three-dimensional interference pattern resulting from interferencebetween the information light and the recording-specific reference lightis formed in the information recording layer 3 of the opticalinformation recording medium 1 to thereby record information. It is thuspossible to record information on the optical information recordingmedium 1 in the form of a three-dimensional interference pattern throughthe use of holography. In addition, the distribution pattern ofmagnetization formed in the information recording layer 3 is easilychangeable. Hence, according to the embodiment, it is possible to recordinformation on the information recording layer 3 so that the informationis erasable in part.

[0098] Furthermore, according to the optical informationrecording/reproducing apparatus 10 of the embodiment, reproduction lightthat carries the information recorded is obtained by irradiating thedistribution pattern of magnetization formed in the informationrecording layer 3 with the reproduction-specific reference light, andthe information can be reproduced by detecting the reproduction light.In addition, according to the embodiment, the direction of polarizationof the reproduction light is orthogonal to the direction of polarizationof the reproduction-specific reference light. It is therefore easy toseparate the reproduction light and the reproduction-specific referencelight from each other by using the polarization beam splitter surface 16a, and the SN ratio (signal-to-noise ratio) of the reproduction signalis thereby improved.

[0099] The present invention is not limited to the foregoing embodiment,and various modifications may be made thereto. For example, the devicefor detecting information recorded on the information recording layer 3may be a smart light sensor in which MOS type solid image pick-updevices and a signal processing circuit are integrated on a single chip(for example, see the literature “O plus E, September 1996, No. 202, pp.93-99”), instead of the CCD array. Since this smart light sensor has ahigh transfer rate and high-speed operation facilities, the use of thissmart light sensor allows high-speed reproduction. For example,reproduction can be performed at transfer rates on the order of Gbit/s.

[0100] Besides, when a smart light sensor is used as the device fordetecting the information recorded on the information recording layer 3in particular, address information and the like need not be recorded onthe address servo areas 6 of the optical information recording medium 1in the form of emboss pits. Instead, a predetermined pattern of addressinformation or the like may be recorded in advance by the same method aswith the holography-based recording on the data areas 7 so that theaddress information or the like be detected by the smart light sensorwith the pick-up under servo operation rendered in the same state asunder reproducing operation. In this case, the basic clock and addressescan be obtained directly from the detection data of the smart lightsensor. The tracking error signal can be obtained from the positioninformation of the reproduction pattern on the smart light sensor. Inaddition, focus servo can be performed by driving the objective lens sothat the reproduction pattern on the smart light sensor becomes maximumin contrast. Besides, under reproducing operation, focus servo can alsobe performed by driving the objective lens so that the reproductionpattern on the smart light sensor becomes maximum in contrast.

[0101] Moreover, the position adjusting device may be rendered capableof changing the position of the pick-up body 12 even in the trackdirection, too.

[0102] Furthermore, in the foregoing embodiment, under the recordingoperation, a half area of the spatial light modulator 18 may be used togenerate the information light while the other half area may be used togenerate the recording-specific reference light.

[0103] As has been described, the optical pick-up device of the presentinvention comprises the pick-up body for at least either recordinginformation on an optical information recording medium on whichinformation is recorded through the use of holography, or reproducinginformation from the optical information recording medium, and positionadjusting means for adjusting the position of the pick-up body in orderto correct a shift in the relative positional relationship between thepick-up body and the optical information recording medium. It istherefore possible to prevent recording and reproduction accuracy fromdeteriorating due to vibrations from exterior and fluctuations in therelative positional relationship between the optical pick-up device andthe recording medium.

[0104] It is apparent from the foregoing description that the inventionmay be carried out in various modes and may be modified in various ways.It is therefore to be understood that within the scope of equivalence ofthe appended claims the invention may be practiced in modes other thanthe foregoing best modes.

1. An optical pick-up device comprising: a pick-up body for at leasteither recording information on an optical information recording mediumon which information is recorded through the use of holography, orreproducing information from the optical information recording medium;and position adjusting means for adjusting a position of the pick-upbody in order to correct a shift in a relative positional relationshipbetween the pick-up body and the optical information recording medium.2. An optical pick-up device according to claim 1, wherein the positionadjusting means changes the position of the pick-up body in a directionperpendicular to a surface of the optical information recording medium,in a direction parallel to the surface of the optical informationrecording medium, and in such a direction as to change an inclination ofthe pick-up body with respect to the surface of the optical informationrecording medium.
 3. An optical pick-up device according to claim 1,wherein the pick-up body comprises: information light generation meansfor generating information light carrying information;recording-specific reference light generation means for generatingrecording-specific reference light; and a recording optical system forirradiating the optical information recording medium with theinformation light and the recording-specific reference light from thesame side so that information is recorded on the optical informationrecording medium in the form of an interference pattern resulting frominterference between the information light and the recording-specificreference light.
 4. An optical pick-up device according to claim 3,wherein the recording optical system performs the irradiation with theinformation light and the recording-specific reference light so that anoptical axis of the information light and an optical axis of therecording-specific reference light are located on the same line.
 5. Anoptical pick-up device according to claim 1, wherein the pick-up bodycomprises: reproduction-specific reference light generation means forgenerating reproduction-specific reference light; a reproducing opticalsystem for irradiating the optical information recording medium with thereproduction-specific reference light and collecting reproduction lightgenerated from the optical information recording medium on the same sideas that from which the optical information recording medium isirradiated with the reproduction-specific reference light; and detectionmeans for detecting the reproduction light collected by the reproducingoptical system.
 6. An optical pick-up device according to claim 5,wherein the reproducing optical system performs the irradiation with thereproduction-specific reference light and the collection of thereproduction light so that an optical axis of the reproduction-specificreference light and an optical axis of the reproduction light arelocated on the same line.
 7. An optical pick-up device according toclaim 1, wherein the pick-up body comprises: information lightgeneration means for generating information light carrying information;recording-specific reference light generation means for generatingrecording-specific reference light; reproduction-specific referencelight generation means for generating reproduction-specific referencelight; a recording/reproducing optical system for irradiating theoptical information recording medium with the information light and therecording-specific reference light from the same side so thatinformation is recorded on the optical information recording medium inthe form of an interference pattern resulting from interference betweenthe information light and the recording-specific reference light, andfor irradiating the optical information recording medium with thereproduction-specific reference light and collecting reproduction lightgenerated from the optical information recording medium on the same sideas that from which the optical information recording medium isirradiated with the reproduction-specific reference light; and detectionmeans for detecting the reproduction light collected by therecording/reproducing optical system.
 8. An optical pick-up deviceaccording to claim 7, wherein the recording/reproducing optical systemperforms the irradiation with the information light, therecording-specific reference light and the reproduction-specificreference light and the collection of the reproduction light so that anoptical axis of the information light, an optical axis of therecording-specific reference light, an optical axis of thereproduction-specific reference light, and an optical axis of thereproduction light are located on the same line.
 9. An optical pick-updevice according to claim 7, wherein the information light generationmeans modulates light spatially, and the detection means detects aspatial modulation pattern of light.